AbstractHydrogenation of milk fat with palladium and nickel as catalysts was studied at various temperatures, pressures, and concentrations of catalyst. Samples were removed from the laboratory hydrogenator at intervals during the reaction, and changes in refractive index, iodine value, Wiley mp, and percentages of fatty acids andtrans‐isomers were determined. Palladium was several times more active as a catalyst than nickel. Milk fat with an iodine value of 35 and mp of 34 C was hydrogenated with 0.05% palladium to an iodine value of 6 and a mp of 46 C in 30 min at 66 C and 53 psi of hydrogen. Kinetic data for each catalyst yielded two slopes, indicating that a change in reaction rate occurred.